Mobile communications devices have become an integral part of society over the last two decades. Indeed, a large percentage of the population owns a mobile communications device, for example, a cell phone. The typical mobile communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.
The typical transceiver includes a power amplifier for amplifying low voltage signals for transmission via the antenna. Given that most mobile communications devices operate on limited battery power, energy efficient power amplifiers may be desirable. More specifically and as will be appreciated by those skilled in the art, Class C and E power amplifiers are common in mobile communications devices since they are efficient power amplifiers. These classes of power amplifiers are more efficient than Class A or B amplifiers, for example, but are subject to performance tradeoffs, for example, they may be nonlinear over certain frequencies and may introduce greater amounts of distortion into the amplified signal (if the signal requires a linear amplifier).
An approach to compensating for this tradeoff is to encode transmitted signals with constant envelope (CE) or continuous phase modulation (CPM) waveforms. These modulations provide for lower energy demands on the power amplifier of the transceiver, for example, by reducing the peak-to-average power ratio (PAPR), increasing average transmit power (providing greater transmission range), and increasing amplifier efficiency.
For example, U.S. Patent Application Publication No. 2008/0039024 to Ikeda et al. discloses an amplifying circuit. The amplifying circuit processes an input orthogonal frequency-division multiplexing (OFDM) signal and provides a pair of CE output signals to provide better power efficiency and less distortion.
When communications devices communicate with each other, the associated waveform exists in a frequency band. Typically, the associated frequency band is standardized and regulated by governmental bodies to prevent unintended interference with other wireless devices. A potential issue that has impacted wireless development is a shortage of unused spectrum. Indeed, as modern communications become more data intensive, wireless operators are scrambling to acquire more spectrum rights to expand network throughput, which has proven to be quite costly.
One approach to this problem is to improve spectral efficiency, i.e. push more data through the allowed frequency band. For example, multiple-input-multiple-output (MIMO) approaches comprise deploying multiple antennas in a device to enhance reception quality and improve data transfer rates.
Another approach is disclosed in “Practical, Real-time, Full Duplex Wireless” by Mayank et al. This approach improves spectral efficiency by transmitting and receiving on the same frequency band. The method includes using a balun transformer coupled to the transmit path to produce an inverted version of the transmitted signal. This inverted signal is summed with the received signal to reduce self-interference.